Add links to docs for addons and top level API (#6555)

This makes it easier to figure out where the docs live.

Googling for e.g. `react-addons-update` also works, but this should
make things easier for people that hyperclick directly to the source.

src/isomorphic/children/ReactChildren.js

@@ -55,6 +55,8 @@ function forEachSingleChild(bookKeeping, child, name) {
 /**
  * Iterates through children that are typically specified as `props.children`.
  *
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.children.foreach
+ *
  * The provided forEachFunc(child, index) will be called for each
  * leaf child.
  *
@@ -146,7 +148,9 @@ function mapIntoWithKeyPrefixInternal(children, array, prefix, func, context) {
 /**
  * Maps children that are typically specified as `props.children`.
  *
- * The provided mapFunction(child, index) will be called for each
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.children.map
+ *
+ * The provided mapFunction(child, key, index) will be called for each
  * leaf child.
  *
  * @param {?*} children Children tree container.
@@ -173,6 +177,8 @@ function forEachSingleChildDummy(traverseContext, child, name) {
  * Count the number of children that are typically specified as
  * `props.children`.
  *
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.children.count
+ *
  * @param {?*} children Children tree container.
  * @return {number} The number of children.
  */
@@ -184,6 +190,8 @@ function countChildren(children, context) {
 /**
  * Flatten a children object (typically specified as `props.children`) and
  * return an array with appropriately re-keyed children.
+ *
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.children.toarray
  */
 function toArray(children) {
   var result = [];

src/isomorphic/children/onlyChild.js

@@ -16,10 +16,13 @@ var invariant = require('invariant');
 
 /**
  * Returns the first child in a collection of children and verifies that there
- * is only one child in the collection. The current implementation of this
- * function assumes that a single child gets passed without a wrapper, but the
- * purpose of this helper function is to abstract away the particular structure
- * of children.
+ * is only one child in the collection.
+ *
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.children.only
+ *
+ * The current implementation of this function assumes that a single child gets
+ * passed without a wrapper, but the purpose of this helper function is to
+ * abstract away the particular structure of children.
  *
  * @param {?object} children Child collection structure.
  * @return {ReactElement} The first and only `ReactElement` contained in the

src/isomorphic/classic/class/ReactClass.js

@@ -740,6 +740,7 @@ var ReactClass = {
 
   /**
    * Creates a composite component class given a class specification.
+   * See https://facebook.github.io/react/docs/top-level-api.html#react.createclass
    *
    * @param {object} spec Class specification (which must define `render`).
    * @return {function} Component constructor function.

src/isomorphic/classic/element/ReactElement.js

@@ -113,6 +113,10 @@ var ReactElement = function(type, key, ref, self, source, owner, props) {
   return element;
 };
 
+/**
+ * Create and return a new ReactElement of the given type.
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.createelement
+ */
 ReactElement.createElement = function(type, config, children) {
   var propName;
 
@@ -230,6 +234,10 @@ ReactElement.createElement = function(type, config, children) {
   );
 };
 
+/**
+ * Return a function that produces ReactElements of a given type.
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.createfactory
+ */
 ReactElement.createFactory = function(type) {
   var factory = ReactElement.createElement.bind(null, type);
   // Expose the type on the factory and the prototype so that it can be
@@ -255,6 +263,10 @@ ReactElement.cloneAndReplaceKey = function(oldElement, newKey) {
   return newElement;
 };
 
+/**
+ * Clone and return a new ReactElement using element as the starting point.
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.cloneelement
+ */
 ReactElement.cloneElement = function(element, config, children) {
   var propName;
 
@@ -335,6 +347,8 @@ ReactElement.cloneElement = function(element, config, children) {
 };
 
 /**
+ * Verifies the object is a ReactElement.
+ * See https://facebook.github.io/react/docs/top-level-api.html#react.isvalidelement
  * @param {?object} object
  * @return {boolean} True if `object` is a valid component.
  * @final